RESUMO
Peroxisomes perform various metabolic processes that are primarily related to the elimination of reactive oxygen species and oxidative lipid metabolism. These organelles are present in all major eukaryotic lineages, nevertheless, information regarding the presence of peroxisomes in opportunistic parasitic protozoa is scarce and in many cases it is still unknown whether these organisms have peroxisomes at all. Here, we performed ultrastructural, cytochemical, and bioinformatic studies to investigate the presence of peroxisomes in three genera of free-living amoebae from two different taxonomic groups that are known to cause fatal infections in humans. By transmission electron microscopy, round structures with a granular content limited by a single membrane were observed in Acanthamoeba castellanii, Acanthamoeba griffini, Acanthamoeba polyphaga, Acanthamoeba royreba, Balamuthia mandrillaris (Amoebozoa), and Naegleria fowleri (Heterolobosea). Further confirmation for the presence of peroxisomes was obtained by treating trophozoites in situ with diaminobenzidine and hydrogen peroxide, which showed positive reaction products for the presence of catalase. We then performed comparative genomic analyses to identify predicted peroxin homologues in these organisms. Our results demonstrate that a complete set of peroxins-which are essential for peroxisome biogenesis, proliferation, and protein import-are present in all of these amoebae. Likewise, our in silico analyses allowed us to identify a complete set of peroxins in Naegleria lovaniensis and three novel peroxin homologues in Naegleria gruberi. Thus, our results indicate that peroxisomes are present in these three genera of free-living amoebae and that they have a similar peroxin complement despite belonging to different evolutionary lineages.
Assuntos
Acanthamoeba castellanii/ultraestrutura , Balamuthia mandrillaris/ultraestrutura , Peroxinas/genética , Peroxissomos/ultraestrutura , Acanthamoeba castellanii/enzimologia , Acanthamoeba castellanii/genética , Balamuthia mandrillaris/enzimologia , Balamuthia mandrillaris/genética , Catalase/metabolismo , Microscopia Eletrônica de Transmissão , Peroxinas/metabolismo , Peroxissomos/enzimologia , Peroxissomos/genética , FilogeniaRESUMO
Baker's yeast is a valuable model system for the study of biological aging as it can be utilized for the measurement of replicative and chronological life spans in response to interventions. Whereas replicative aging in Saccharomyces cerevisiae mirrors dividing mammalian cells, chronological aging is seen in non-dividing cells. Aging is strongly influenced by the cellular organelles, especially by mitochondria which house essential functions like oxidative phosphorylation. Additionally, peroxisomes were shown to modulate the aging process, mainly by their turnover of reactive oxygen species. There is a fundamental interest in understanding how mitochondria and peroxisomes contribute to cellular aging. This work analyzes chronological aging in yeast mutants that are affected in peroxisomal proliferation and inheritance. Deletion of INP1 (retention of peroxisomes in the mother cell) or PEX11 (division of peroxisomes) leads to clearly reduced life spans compared to the wild-type control under conditions which depend on peroxisomal metabolism. Δinp1 cells are long-lived in contrast to the wild type and Δpex11 when assayed under conditions that not necessitate peroxisome function. Neither treatment affects the index of respiratory capacity, indicating fully functional mitochondria. Evaluation of stress resistances reveals that Δinp1 has significantly higher resistance to the apoptosis elicitor acetic acid. Old Δpex11 cells from an oleate culture are more susceptible to hydrogen peroxide treatment compared to Δinp1 and the wild type. Finally, aged cells are hyper-sensitive to heat shock treatment in contrast to young cells.